It is recognized that superalloy materials are among the most difficult materials to weld due to their susceptibility to weld solidification cracking and strain age cracking The term “superalloy” is used herein as it is commonly used in the art, ie, a highly corrosion and oxidation resistant alloy that exhibits excellent mechanical strength and resistance to creep at high temperatures Superalloys typically include a high nickel or cobalt content. Examples of superalloys include alloys sold under the trademarks and brand names Hastelloy, Inconel alloys (e.g., IN 738, IN 792, IN 939), Rene alloys (e.g, Rene N5, Rene 80, Rene 142), Haynes alloys, Mar M, CM 247, CM 247 LC, C263, 718, X-750, ECY 768, 282, X45, PWA 1483 and CMSX (eg, CMSX-4) single crystal alloys.
It is known to utilize selective laser melting (SLM) or selective laser sintering (SLS) to melt a thin layer of superalloy powder particles onto a superalloy substrate. The melt pool is shielded from the atmosphere by applying an inert gas, such as argon, during the laser heating These processes tend to trap the oxides (e.g., aluminum and chromium oxides) that are adherent on the surface of the particles within the layer of deposited material, resulting in porosity, inclusions and other defects associated with the trapped oxides Post process hot isostatic pressing (HIP) is often used to collapse these voids, inclusions and cracks in order to improve the properties of the deposited coating. The application of these processes is also limited to horizontal surfaces due to the requirement of pre-placing the powder
Laser microcladding is a 3D-capable process that deposits a small, thin layer of material onto a surface by using a laser beam to melt a flow of powder directed toward the surface. The powder is propelled toward the surface by a jet of gas, and when the powder is a steel or alloy material, the gas is argon or other inert gas which shields the molten alloy from atmospheric oxygen. Laser microcladding is limited by its low deposition rate, such as on the order of 1 to 6 cm3/hr Furthermore, because the protective argon shield tends to dissipate before the clad material is fully cooled, superficial oxidation and nitridation may occur on the surface of the deposit, which is problematic when multiple layers of clad material are necessary to achieve a desired cladding thickness.
FIG. 1 is a conventional chart illustrating the relative weldability of various superalloys as a function of their aluminum and titanium content. Alloys such as Inconel® IN718 which have relatively lower concentrations of these elements, and consequentially relatively lower gamma prime content, are considered relatively weldable, although such welding is generally limited to low stress regions of a component Alloys such as Inconel® IN939 which have relatively higher concentrations of these elements are much more difficult to weld A dashed line 10 indicates a recognized upper boundary of a zone of weldability The line 10 intersects 3 wt. % aluminum on the vertical axis and 6 wt. % titanium on the horizontal axis. Alloys outside the zone of weldability are recognized as being very difficult to weld with traditional processes, and the alloys with the highest aluminum content are generally found to be the most difficult to weld, as indicated by the arrow